Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $233.37   12.335%   $262.1562   $262.16   $262.15   $262.20  
  Purchase #2 $97.39   11.109%   $108.2091   $108.21   $108.20   $108.20  
  Purchase #3 $59.88   5.195%   $62.9908   $62.99   $63.00   $63.00  
  Purchase #4 $181.98   5.250%   $191.534   $191.53   $191.55   $191.50  
  Purchase #5 $205.77   10.745%   $227.88   $227.88   $227.90   $227.90  
  Purchase #6 $50.92   11.575%   $56.814   $56.81   $56.80   $56.80  
  Purchase #7 $17.85   10.351%   $19.6977   $19.70   $19.70   $19.70  
  7 purchase totals = $847.16       $929.2818   $929.28   $929.30   $929.30